There has been constant demand for further sensitivity improvement in silver halide grains.
As a means of meeting this demand, grains such as those disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 143331/1985 are available, which are so-called core-shell grains, wherein the silver iodide content in the inner portion is higher than that in the outer portion.
Later, investigations were made for more constant obtainment of the effect of high sensitivity. Silver halide grains having no failures in the inner phase containing silver iodide, a highly uniform silver halide composition and a narrow silver iodide distribution among the grains has been prepared stably by a method based on solubility product differences between different kind of silver halide, such as that disclosed in Japanese Patent O.P.I. Publication Nos. 167537/1990, affording the production of a silver halide photographic light-sensitive material (hereinafter also referred to as light-sensitive material) of high sensitivity and excellent graininess.
However, the light-sensitive materials incorporating such grains posed a new problem of granularity deterioration in long-term storage, which had not been predictable in conventional grains.